1. Field of the Invention
The present invention relates to an accumulator for vehicles, and more specifically, to an improvement in an accumulator having an oil chamber, a gas chamber, and metal bellows therein.
2. Description of the Related Art
Prior art accumulators for motor vehicles, which are adapted to contain oil and compressed gas, comprise a housing and a rod fitted therein. A gas chamber and an oil chamber are defined inside the housing. High pressure compressed inactive gas, such as nitrogen, is charged in the gas chamber. The repulsive force of the gas acts as a gas spring mechanism. Damping-force generating means is provided inside the housing. The oil in the oil chamber is subjected to viscous resistance as it passes through the generating means, so that reciprocation of the rod is damped.
A conventional accumulator of this type can have a partition member made of elastomer, which partitions the housing into a gas chamber and an oil chamber. The partition member, which is made of elastomer, allows the passage of a gas from the gas chamber into the oil chamber, though in a small amount. Hence, the pressure of the gas in the gas chamber falls after a long use of the accumulator.
To prevent this fall of gas pressure, it has been proposed that the partition member be replaced by metal bellows which are a more effective gas barrier.
However, since metal has a lower elastic limit than elastomer, the metal bellows will be permanently deformed if a high-pressure gas is charged. Once deformed, the bellows becomes too weak to perform its function or can no longer perform its function.
Hitherto, use has been made of metal bellows whose wall is thick enough to withstand the pressure of the gas being charged into the gas chamber. However, the thicker the bellows, the greater stress the bellows will have when the bellows expands or contracts. To reduce this stress, the bellows must have more convolutions. If the bellows have more convolutions, their axial length will be inevitably long.